Influence of garnet hosts on the Raman spectra of quartz inclusions

Abstract

Raman spectra of five natural garnet grains with compositions close to those of the endmember species almandine, spessartine, pyrope, grossular, and andradite were measured. Spectral data for the garnet grains are used to study the interference with the three intense peaks from quartz (labeled as Q01, Q02, and Q03 in order of decreasing wavenumber) that are usually employed in quartz Raman barometry. The peaks from grandite garnet do not interfere with these three peaks from quartz. The pyralspite garnet spectrum has a clear peak at 209-221 cm^-1 that significantly interferes with the Q02 peak from quartz. Quartz Raman barometry is usually applied to a quartz inclusion in a garnet host. To avoid interference of the host garnet spectrum on the quartz Raman barometry results, it is strongly recommended that spectra with less intense garnet peaks are considered, e.g., with I_G05 < I_Q02, where I_G05 and I_Q02 denote the normalized intensities of the most intense peak from the pyralspite garnet (labeled G05) and the Q02 peak from quartz, respectively.